The present application describes systems and techniques relating to secure delivery of encrypted digital content.
Conventional encryption/decryption technologies use various techniques to securely deliver encrypted digital content (e.g., music, movies, images, text) to a media player, such as a software application (e.g., RealPlayer, Windows Media Player) residing on a client computer system or a media player device (e.g., a digital versatile disk (DVD) player, a satellite signal decoder box). Generally, these techniques involve increasing the difficulty and/or computational expense of breaking the encryption scheme. Commonly used techniques include increasing an encryption scheme's complexity, using device authentication and authorization protocols, software obfuscation (i.e., making the decryption software difficult to reverse engineer), and reducing accessibility of encryption keys.
Common encryption schemes include asymmetric encryption and symmetric encryption. In symmetric encryption (AKA common key cryptology), the same key is used to encrypt and decrypt information. In asymmetric encryption (AKA public key cryptology), a public key is used to encrypt the information and a private key is used to decrypt the information (e.g., Pretty Good Privacy (PGP)).
Device authentication protocols typically involve an exchange of digital certificates. A digital certificate is an electronic attachment to a message commonly used to identify the message sender. Digital certificates are typically implemented using a public-key-based digital signature algorithm.
Device authorization protocols typically involve a central authority maintaining and transmitting access information defining which devices are authorized to access encrypted content.
A common software obfuscation technique is referred to as “spaghetti coding” in which the software is purposefully written to include an excessive number of jumps or branches, irrelevant code, self-modifying code, and the like. Other software obfuscation techniques include merging application data and instructions into the same address space, and setting debugger traps that discourage setting of breakpoints by a debugger program.
A “trusted” media player is one that, to a reasonable degree of certainty, will present content only to an authorized customer and will prevent the content from being obtained and saved in an unencrypted form. A media player includes software, or a combination of software and hardware, that implements a decryption and authorization scheme. Trusted media players typically use software obfuscation to discourage users from tampering with the media player to gain unauthorized access to encrypted digital content.
Moreover, some encryption schemes may depend on restricting access to the decryption software and hardware in a media player to discourage reverse engineering. For example, in real-time data exchange situations (e.g., streaming digital content on the Internet), typical encryption techniques include key handshakes, dynamic key exchange, and random key challenges. The security of these techniques typically depends on the decryption software and hardware being made available only to manufactures of media player devices.
Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages may be apparent from the description and drawings, and from the claims.